'nil is not ()

The truth value of 'nil is "true". This is kind of counter-intuitive,
at least for someone coming from an Elisp background.

In Emacs Lisp I get this behavior:

  (mapcar
    (lambda (value)
       (not (not value)) )
    '(foo t nil ()) )
  => (t t nil nil)

In Sawfish the equivalent evaluates to

  => (t t t ())

In more concrete terms, I would like the following to DWIM:

  (let ((stuff '(("foo" t nil 15)
                 ("bar" nil t 22) )) )
     (... do something with this stuff) )

A simple workaround is to use () instead of nil (or backquotes and
,nil ;-) but the real problem is that discovering the false assumption
that 'nil is not true can be hellish (signed, been there, done that,
several times).

I'm not enough of a Lisp guru to tell which is "right" but it would be
nice if it were consistent between Sawfish and Emacs. Is there
someplace I can tweak this behavior? Or is this perhaps changed in
newer versions of Sawfish? I'm using the Debian "stable" version on
top of an old Ximian, which is predictably not exactly spanking new.
(sawfish .deb 1.0.1.20020116-3, librep9 .deb 1:0.15.2-1.ximian.1,
rep-gtk .deb 0.15-ximian.7 -- the stuff before the dash is usually the
upstream version number, removing any prefix which ends in a colon;
so, that would be sawfish 1.0.1, librep9 0.15.2, rep-gtk 0.15)

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